Data synthesis
We performed statistical analyses using Review Manager 5 Software (version 5.3) and Stata (version 15.1). For dichotomous data, we calculated risk ratio (RR) with 95% confidence interval (CI) by using the Mantel-Haenszel approach. For continuous outcomes, we calculated mean differences (MD) with 95% confidence intervals using an Inverse Variance method. A P value of < 0.05 was considered statistically significant. Summary effects estimates were calculated using DerSimonian and Laird random-effects models.16We performed subgroup analysis on the basis of lubricants type, parity, overall risk of bias, birthweight and ethnicities when sufficient data for each subgroup. An interaction analysis (P for interaction) was performed to evaluate the difference between subgroups. Statistical heterogeneity was evaluated using the I2 statistic and Cochran Chi-square test. Publication bias was assessed visually by funnel plots and quantitatively with Begg’s test for asymmetry.17 Sensitivity analysis was also undertaken to examine the effect of a single study on the overall effect size and the robustness of results with omitting one study at a time.